Contrasting coordination behavior of Group 12 perchlorate salts with an acyclic N3O2 donor ligand by X-ray crystallography and 1H NMR

Abstract

An unbranched N₃O₂ ligand 2,6-bis[((2-pyridinylmethyl)oxy)methyl]pyridine (L1) was used to prepare new mononuclear heteroleptic Group 12 perchlorate complexes characterized by IR, ¹H NMR and X-ray crystallography. Racemic complexes with pentadentate L1 and one to four oxygens from either water or perchlorate bound to a metal ion were structurally characterized. Octahedral [Zn(L1)(OH₂)](ClO₄)₂ (1) and pentagonal bipyramidal [Cd(L1)(OH₂)(OClO₃)]ClO₄ (2) structures were found with lighter congeners. The polymorphic forms of [Hg(L1)(ClO₄)₂] characterized (3 in P and 4 in P2₁/c) had a mix of monodentate, anisobidentate and bidentate perchlorates, providing the first examples of a tricapped trigonal prismatic Hg(II) coordination geometry, as well as additional examples of a rare square antiprismatic Hg(II) coordination geometry. Solution state ¹H NMR characterization of the Group 12 complexes in CD₃CN indicated intramolecular reorganization remained rapid under conditions where intermolecular M–L1 exchange was slow on the chemical shift time scale for Zn(II) and on the J(M¹H) time scale for Cd(II) and Hg(II). Solution studies with more than one equivalent of ligand also suggested that a complex with a 1 : 2 ratio of M : L1 contributed significantly to solution equilibria with Hg(II) but not the other metal ions. The behavior of related linear pentadentate ligands with Group 12 perchlorate salts is discussed.